Growing plants need nitrogen. Plants such as maize (Indian corn) require a substantial quantity of nitrogen. The soil corn plants grow in obtains nitrogen from legumes such as soybeans, from snow and from other sources. Excess nitrogen will reduce yield of crops such as corn. Insufficient nitrogen will also reduce crop yield. Water used to irrigate plants generally contains minimal nitrogen.
Anhydrous ammonia has been used for many years to provide nitrogen. The anhydrous ammonia is injected into the ground as a liquid or vapor. Injection of anhydrous ammonia into soil is subject to a number of problems. Determining the quantity of nitrogen to be added is complicated by the fact that a substantial quantity of nitrogen may be stored in the soil. Soil samples are required to determine the status of stored nitrogen that is available. The soil samples often indicate that the distribution of stored nitrogen varies from one location to another in each farm field.
Anhydrous ammonia is one of the most efficient sources of nitrogen fertilizer for plant growth. Under atmospheric temperature and pressure anhydrous ammonia is a colorless gas. The gas is compressed into a liquid state for agricultural use. The liquid state can be maintained by pressure, by cooling or a combination of pressure and cooling. The equilibrium vapor pressure at sixty degrees Fahrenheit in a pressure tank is ninety three pounds per square inch (psi).
The cost of anhydrous ammonia has increased overtime due in part to the increased use by farmers around the planet. Farmers have in the past applied anhydrous ammonia and other fertilizers to maximize crop yield. Farmers are forced today to consider the costs and reduce the use of anhydrous ammonia and other fertilizers, when the cost of additional fertilizers exceeds the value of a minimal increase in crop production.
The loss of anhydrous ammonia needs to be limited to the extent possible. The over application in some areas of each field may also need to be limited or even eliminated.
The change in some anhydrous ammonia from a liquid to a vapor makes accurate control of the application rate difficult. Vapor separated from the liquid results in the over application rate in some areas. The separation of vapor may also result in the loss of some anhydrous ammonia.
Increased pressure in an anhydrous ammonia application system can keep the pressure of the liquid above the vapor pressure of the liquid at ambient temperatures. However, a pump in the supply system between a nurse tank and liquid discharge nozzle will create a pressure drop on the pump inlet side. This pressure drop will at times produce vapor. The anhydrous ammonia vapor will prevent accurate metering of a liquid and vapor mixture. Separation of the vapor generally results in a loss of some anhydrous ammonia.
Reducing the temperature in an anhydrous ammonia application system can keep the temperature of the liquid below the temperature at which vapor could be formed. Temperature lowering is obtained by bleeding off some liquid, expanding the liquid into a cold vapor and passing the cold vapor through a heat exchanger. Anhydrous ammonia liquid passing through the heat exchanger is cooled. The vapor discharged from the heat exchanger is then injected into the ground. The vapor is not completely lost. However, some anhydrous ammonia vapor is added to one of several plant rows that also receives a metered quantity of liquid anhydrous ammonia. The additional anhydrous ammonia from vapor may provide excess nitrogen to one crop row and may change crop yield in that crop row.
Anhydrous ammonia application systems with or without pumps as well as systems with or without cooling systems often include a flow sensor that measures the total flow rate. These systems include a servo valve that controls the total flow rate. A manifold divides the flow of anhydrous ammonia to soil cutting knives. The servo valve reduces the pressure of discharged anhydrous ammonia and may create some vapor. Vapor mixed with liquid anhydrous ammonia will result in an unequal flow from a manifold distributor downstream from a servo valve or other flow control device.
A number of additional distribution problems may occur. Some of these problems are obvious to an operator without a sensor warning. A broken line between a supply tank and the distributor will generally create a visible cloud. A disconnect of an anhydrous ammonia tank would be obvious. The location of the disconnected trailer and tank would indicate where fertilizer application stopped. A plugged distribution line is however difficult to detect without a suitable monitor system.
The liquid passes through various pipes and devices from the pressure tank to a manifold or distributor. The distributor divides the anhydrous ammonia liquid flow into a plurality of lines each of which is connected to a knife that opens a furrow in the ground. The furrow receives the anhydrous ammonia liquid and vapor and retains the nitrogen. The distributor divides liquid anhydrous ammonia into substantially equal flow through each line. However, if there is significant vapor mixed with the liquid, the distributor will not discharge equal quantities of fertilizer into each line.
The devices between the pressure tank and the distributor varies from one fertilizer distributor system to another. The devices include off-on valves, flow measurement devices, metering valves, vapor separators, coolers, pumps, orifices, filters and other devices. Each of these devices may create a pressure drop. The pressure drops may create anhydrous ammonia vapors.
Anhydrous ammonia applicators, with a large number of distribution lines and knives that open furrows, require flow splitters. The flow splitters divide the flow of liquid fertilizer into two or more equal fluid streams each of which is connected to a distributor. Distributors may be referred to as manifolds. Distributors have a limited number of discharge line ports. The number of distributors employed depend on the number of discharge ports in each distributor and the total number of furrow opening knives on the tool bar of the applicator. The flow splitters also produce pressure drops.
The lines from a distributor to the knives are relatively long and extend along a tool bar or applicator frame. Tool bars and applicator frames often have wings that pivot up and down to follow the surface of a field. Each of the knives may be mounted on a shank that moves relative to the frame. The lines from the distributor to the knives or other furrow openers are subjected to the movements of the knives relative to the distributor. The discharge end of each line is also subjected to soil moved by the knives, crop material on the ground, and possible freezing or plugging. The movements of the lines may decrease the size of the inside passage, wear a hole in a line or even sever a line.
The number of lines extending from each distributor to each of the knives and the small quantity of anhydrous ammonia passing through each line renders visual line monitoring difficult for an operator of an applicator. An applicator may have more than twenty four lines extending from two or more distributors. All of the lines extending from one distributor have a uniform length that is the same length as the length of the line to a knife that is the greatest distance from the distributor. The length of lines extending from one distributor are the same so that the pressure of anhydrous ammonia in the distributor forces the same quantity of fertilizer into each line. Lines with equal diameter and length have nearly the same resistance to flow, if the knives and lines are substantially identical to each other.
All of the liquid and vapor exiting a manifold through a distribution line will flow to a knife unless there is a failure in the distribution line and knife assembly. The distribution lines are generally available for a visual inspection. Operators inspect the distribution lines from time to time.